In what follows the axis of revolution of a raw blank will be called its axis. This axis defines an axial direction of the blank and of the device for shaping the blank when considering the blank in position on the device.
A raw tire blank or green tire is generally formed of a carcass on which a crown assembly intended to form the tread is positioned. The carcass and the crown assembly are formed of unvulcanized rubber profiled elements some of which contain reinforcing threads.
When the blank is vulcanized in a mould, a variation in the relative positioning of the carcass and of the crown assembly is observed. The final relative position of the carcass and of the crown assembly is dictated by the mould, and is therefore known. The variation in the relative positioning allows certain geometric features of the vulcanized tire to be modified. Thus, these geometric features can be controlled by modifying the initial relative position of the carcass and of the crown assembly, the final relative position and the variation in relative positioning also being known.
The tire crown assembly blank comprises crown reinforcing plies formed of reinforcing threads coated in rubber, which are parallel to one another and make a given angle with the circumferential direction of the tire, the tread, and a certain number of rubber profiled elements which are intended to reinforce the axial ends of the reinforcing plies.
The raw blank of the crown assembly is formed on a blank shaping device. This device comprises a plurality of elements for shaping a circumferential portion of the tire crown blank. Each element comprises a bearing surface for bearing radially against a circumferential portion of the radially internal surface of the blank. Each bearing surface is carried by a support that positions the element with respect to the blank.
In order to modify the initial relative position and therefore the geometric features of the tire, the bearing surface of the device exhibits, in a radial plane, for given geometric features, a given profile that determines the initial relative position. In order to obtain a wide variety of geometric features, it is necessary to have a wide variety of profiles for the bearing surfaces of the elements of the device.
Now, changing the elements in order to build different types of tire that have different geometric features is time-consuming. In addition, these elements are relatively expensive.